1. Field of the Invention
The invention relates to a windshield wiper control unit and a windshield wiper control method that are used to control the operation of a windshield wiper based on the position of an operation member.
2. Description of the Related Art
For example, Japanese Patent Application Publication No. 10-315919 (JP-A-10-315919) describes a windshield wiper control unit that controls the intermittent wiping cycle of a windshield wiper in response to an operation performed on an operation knob. According to JP-A-10-315919, a volume device of which the resistance value continuously changes in response to the operation performed on the operation knob is used, and a detection signal indicating the position of the operation knob is obtained based on the resistance value of the volume device.
Japanese Patent Application Publication No. 2006-321285 (JP-A-2006-321285) describes a windshield wiper control unit that is similar to the windshield wiper described above. The windshield wiper control unit according to JP-A-2006-321285 stores the learned value of the resistance value of the volume device, computes the learned value based on a signal output from the volume device, and corrects the positional information that indicates the position of the volume device based on the result of computation.
The resistance value of the volume device varies from product to product. Therefore, when a detection signal is obtained based on the resistance value as described in JP-A-10-315919, even if a user rotates the operation knob to a desired position, the windshield wiper may fail to operate as the user expects due to the variation in the resistance value.
The configuration described in JP-A-2006-321285 is made with the product-to-product variation in the resistance value of the volume device taken into account. However, the described correction may be made only when the accurate position of the volume device can be obtained. Accordingly, with the configuration described in JP-A-2006-321285, it is not possible to compensate for changes or errors in the resistance value due to the temperature environment under which the product is used or A/D conversion, or changes in the characteristics of the resistance value over time after shipment.